This invention relates to hydraulic drive mechanisms and more particularly to hydraulic drive mechanisms for driving reactivity control mechanisms in nuclear reactors.
As is well known in the art, a nuclear power plant generates electricity from heat produced by fissioning of nuclear material. The nuclear material is contained within fuel assemblies which comprise the core of a nuclear reactor. As the reactor coolant is circulated through the nuclear reactor core heat is transferred from the core to the reactor coolant which is then conducted to a remote location for generating steam and electricity in a conventional manner.
Control of the nuclear reactor is usually achieved by control rods which are dispersed throughout the nuclear reactor core and are mounted for movement into and out of the core. The control rods function by absorbing excess neutrons produced by the nuclear reaction. In addition to control rods, a nuclear reactor may also have displacer rods disposed therein which are also mounted for movement into and out of the core to effect reactivity of the core as described in copending U.S. patent application Ser. No. 217,060 filed Dec. 16, 1980 in the name of W. J. Dollard et al. entitled "Mechanical Spectral Shift Reactor" and assigned to the Westinghouse Electric Corporation.
After a period of operation of a nuclear reactor, it is necessary to be able to access and replace the spent fuel assembles in the reactor with fresh fuel assemblies. During this operation, it is necessary to remove the reactor vessel closure head so as to be able to access the fuel assemblies in the nuclear reactor core. Since the control rods and displacer rods are attached to their respective drive mechanisms which are mounted on the reactor vessel closure head, it is expedient to disconnect the control rods and displacer rods from their corresponding drive mechanisms before removing the reactor vessel closure head while maintaining the control rods and displacer rods in the nuclear reactor core.
The ability of leaving the control rods and displacer rods in the nuclear reactor core during refueling may be achieved by providing a disconnect mechanism between the control rod and the control rod drive mechanism. One such disconnect mechanism is disclosed in U.S. Pat. No. 4,147,589, entitled "Control Rod for a Nuclear Reactor", issued Apr. 3, 1979 in the name of W. G. Roman et al. and assigned to the Westinghouse Electric Corporation. In the patent to Roman et al., there is described a control rod assembly for a nuclear reactor having a remotely disengageable coupling between the control rod and the control rod drive shaft. The coupling is actuated by first lowering then raising the drive shaft. The described motion causes actual repositioning of a pin in a grooved rotatable cylinder, each being attached to different parts of the drive shaft which are axially movable relative to each other. While the patent to Roman et al. describes one mechanism for disconnecting a drive mechanism from a reactivity control mechanism in a nuclear reactor, there is needed an alternative and simple mechanism for effecting such a disconnection.